Desulfurization of hydrocarbon oils with vanadium oxide catalyst in the presence of naphthenes



United States Patent DESULFURIZATION 0F HYDROCARBON OILS WITH VANADIUM DXIDE CATALYST IN THE PRESENCE OF NAPHTHENES William F. Arey, Jr., and Charles N. Kimberlin, Jr., Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application September 4, 1951, Serial No. 245,076

Claims. 01. 196-48) The present invention relates to the treatment of sulfurcontaining organic materials, in particular, sulfur-bearing hydrocarbon material, to desulfurize the same. More particularly, the present invention relates to the desulfurization of sulfur-containing petroleum fractions, in particular fractions containing ring type sulfur compounds.

The problem of sulfur removal from petroleum fractions and crudes is as old as the petroleum industry. For most purposes, it is undesirable to have an appreciable amount of sulfur in any petroleum products. Gasoline should be relatively sulfur-free to make it compatible with lead. Motor fuels containing sulfur as mercaptans are undesirable because of odor and gum formation characteristics. Sulfur is objectionable in fuel oils of any kind because it burns to form S02 which is obnoxiops and corrosive. 1

Sulfur occurs in petroleum stocks, generally i'n two main forms, as mercaptans and as part of a more or less substituted ring, of which thiophenef is the prototype. The former type is generally found in the lower boiling fractions, in the naphtha, kerosene, and light gas oil material, whereas the ring-sulfur compounds form the bulk of the sulfur-bearing material of the higher boiling petroleum fraction. Numerous processes for sulfur removal from relatively low molecular and lower boiling fractions have been suggested, such as doctor sweetening, wherein mercaptans are converted to disulfides, caustic treating, solvent extraction, copper chloride treating, etc., all of which give a more or less satisfactory decrease in sulfur or inactivation of mercaptans by their conversion into disulfides. The latter remain in the treated product, and must be removed if it is desired to obtain a sulfur-free product.

Sulfur removal from petroleum fractions containing ring-type sulfur compounds, however, has been a much more difficult operation. Such sulfur is, of course, not susceptible to chemical operations satisfactory with mercaptan sulfur.

One satisfactory method for removing sulfur from products wherein it is present as a ring-type compound has been by hydrogenation in the presence of a so-called sulfactive catalyst. Thus, it has been found that certain catalysts, such as cobalt molybdate, tungsten sulfide, nickel sulfide, molybdenum sulfide, etc., are good hydrogenation catalysts and that when these catalyst substances are employed in the hydrogenation of sulfur-containing petroleum stock, these catalysts are not poisoned by sulfur but, on the contrary, tend to reduce the sulfur content of the material being hydrogenated, the sulfur being removed as HzS. The use of hydrogen, however, is not always feasible nor available, particularly in smaller refinery establishments. For its preparation there is required expensive equipment, as a catalytic methane reforming or a carbonsteam or iron-steam plant, as well as compressors, distribution means and the like. Because of this, hydrogenation of sulfur-containing crudes has added materially to the processing costs and, in many cases, it is more economical to market a lower quality sulfur-containing prod- 2,760,906 Patented Aug. 28, 1956 uct at a low price to meet the competition of a crude from an oil field containing little sulfur, than it is to undertake to hydrogenate this crude.

The present invention relates to a novel process for removing catalytically sulfur of the ring type from sulfurcontaining crude and distillates without the necessity of adding extraneous hydrogen, by a process involving a transfer of hydrogen from a hydrogen donor compound to the sulfur compound. It has been discovered that sulfur-containing fractions may be freed of substantial amounts of such sulfur by contacting the sulfur-containing materials in the presence of a compound adapted for use as a hydrogen donor in a hydrogen transfer reaction. Among the hydrogen donors found to be most practicable are the naphthenes.

This invention further dilfers from conventional hydrogenation reactions in that molecular hydrogen is not supplied to the reaction as such, but is supplied in situ from a hydrogen donor such as a naphthene or an isoparafiin. The invention is especially applicable to catalyzed reactions in which hydrogen is directly transferred from the hydrogen donor to the sulfur being removed from the organic molecule. In general, the sulfur removed from the'organic compounds is subsequently converted by the hydrogen transfer reaction to a sulfide, usually hydrogen sulfide. Generally, the hydrogen transfer reaction is carried out in the vapor phase with the use of a catalyst. The use of the selective catalyst results in much greater selectivities in the removal of sulfur to give the desired sulfur-free products and a substantial reduction in undesirable degradation reactions of the starting materials to gaseous products and carbonaceaus by-products.

Naphthenes can be defined as saturated compounds of the general formula C2H2n having closed links composed of methylene groups. The naphthenic hydrocarbons which can be employed as hydrogen donors may be those having six cyclic carbon atoms or more, that is, cyclohexane and its derivatives. Naphthenic rings having four or less carbon atoms are too unstable to function satisfactorily. Alkylated derivatives of these naphthenes such as methylcyclohexane can also be employed. During the course of the reaction, the naphthenes are dehydrogenated to produce aromatic type products. For instance, when cyclohexane is used, it is converted to benzene and when methylcyclohexane is used, it is converted to toluene. The hydrogen atoms which are thus. removed from the naphthenes are catalytically utilized in the presence of the catalyst to combine with the sulfur'present as organically bound sulfur in the feed stock, thereby removing the sulfur from the feed stock and converting it into an easily separable form. Cyclohexane and its higher homologues are particularly adapted for use in the role of hydrogen donors because the removal of six hydrogen atoms from cyclohexane converts it to the completely f aromatized benzene.

The reaction is carried out in vapor phase in the presence of the catalyst and under conditions of temperature, pressure, feed rates, and the like, so chosen as to produce the maximum possible removal of sulfur from the feed stock and at the same time to obtain high selectivity and relatively pure final sulfur-free products. The equipment employed for this process may be of any type known to those skilled in the art for effecting a vapor phase catalytic reaction. Thus, for example, liquid feed is charged to a vaporizer fromwhich the resulting feed vapors pass through a preheatingi zone and thence into the catalytic reaction zone iniwhi'ch the vapors are contacted with the catalyst.

reaction product and non-condensible gases.

The catalyst which has been found to be particularly useful 'in carrying out the reaction to remove organically bound sulfur is a'specially prepared vanadiunroxide cat-' alyst supported on alumina. The use of vanadium catalysts for certain specific refinery operations has previously been suggested, for instance, hydroforming and isomerization and'the like. In these operationsit has been. the general equivalent of related compounds such as molyb denum, chromium and the like These processes are generally ones involving added'hydrogen, andthe catalystsgenerally have behavior and activities of a comparable nature. In the present invention, however, involvinga hydrogen transfer from a naphthene to a thiophene, probablytoform an unstable tetrahydrothiophene which is then: cracked with the evolution of H28, not only is the catalyticraction specific to the vanadium, butalso to the natureof .thecarrier; furthermore, the reaction is specific tothemanneLWhereby the catalyst is prepared, for two catalysts having the same composition, but differing only in themanner. of .preparation have quite. different properties. as hydrogen transfer catalysts, as will be made more clear. below-..

In order to. reactivate the. catalyst, carbonaceous deposits-are removed andthe catalyst regenerated by a strippingsprocessaas With steam, nitrogen, flue gas and thelike, at elevated .temperaturesof about 1300-1600 F. Also, the organic mattermay be burnedoif directly Withair. In its ease of regeneration, the catalyst has a decided. advantage over such materials. as activated carbon, vor catalysts supported on activated carbon.

The desulfurized reactionmixture is taken from the catalytic reaction; zone and preferably condensed to a liquid comprising-the reactionproducts and non-condensible'gases. Theliquid reaction product so obtained can bezworkedup inany suitablemauner, for example, by.

fractionation, adsorption, or, crystallization, to recover both the-desulfurized feed and the aromatized hydrogen donor, awell as'anyv hydrogenated product present as the resultof the use: of. unsaturates in .the reaction. Any hydrogenrsulfide'presentin the liquid may be removed by-- extraction, caustic :washing, or by other'conventional methodsxfor. removal: of hydrogen sulfide. Unchanged or-zincompletely, desulfurized reactants can be recycled, together. with freshsulfur-containing ,feed and fresh hydrogen donor material. If desired, an inert diluent such as; :for example, a portion of. .the non-condensible gaseous products. canbe' employed; It is also possible to recycle.- Although there is a part. of. the producttasija diluent. nornecessity-'for...=a diluent in order; to obtain the desired featuressof. the.reaction,,the.use: of some such inert materialmay: at timesabedesirable to effect more efficient andsimpler control. of. the reaction.

Itwill beunderstood that the. exact conditions ernployed: in .carryingzout the desulfurization reaction will bezdetermined by the" nature; of the. feed' constituents, the desiredextentcofr removalofisulfur per pass, and the exactcatalyst being employed. Thegreaction may be-carriedout underpressures ranging from atmospheric tosuperatmospheric with the restriction. that the reaction must:he carried out'imthe'vapor. phase. The; range of pressures may varyv frornto. 200 p. s. i. g. andhigher.

In general, therange of'temperaturesfor car ying outthe desulfurization reaction is: of the order'of 6009-1 100 F. Optimumvtemperatures: for the-reaction are; consid ered to beabout.750."-95'0 F. Atztemperatures' belowthis range, the, ratetoffreaction' tends, to fall olf'and becomesomewhat. slowand: the; removal of. sulfur is. substantially: incomplete, even after adequate contact with thezzcatalyst. At: temperatures .higherthan this limit,

there is: noticedian increased. tendency towards; the occurrence of. side: reactions. such as thermal cracking, gas. formation; polymerizatiomgandt other undesirable reacbe relatively short, such as 0.1 to 1 second, to achieve optimum selectivity and-satisfactory removal of su-lfur.-

ized. This may be determined by ascertaining the naphthene content of the feedand, if'necessary, augmenting thiswith extraneous naphthenes, such as cyclohexane, etc.

As to the types of sulfur-containing feed stocks which may be desulfurized by this novel hydrogen transfer reaction, these include various types of organic materials having organically bound. sulfur suchfas thiophene, alkylated thiophenes, and other thiophene derivatives, diethyl sulfide, diethyl disulfide, dipropyl sulfide, dibutyl sulfide, diamyl sulfide,- mercaptans, various types of sulfur acids, etc. The-process isespecially useful for desulfurizing petroleum fractions, as for instance, naphtha fractions containing organically bound sulfur which must be removed before the fractions can be used for many purposes. In general, compounds must be used whose desulfurized products are sufiiciently stable to withstand the relatively high temperatures and yet emerge from the reaction zone as intact molecules.

The. process may be executed in a batch or continuous manner. Generally, better conversions are obtained with multipassprocesses. The catalyst may be employed in a fixed bed, movingbed, or in a fluidized manner, depending on the type of operation desired.

This invention will'be better understood with reference niurnmeta vanadate followed by subsequent conversion of the ammonium vanadate to vanadium oxide by heat. A good way of preparing the catalyst is as follows:

Aluminum amylate washydrolyzed by the addition of water to give an aqueous slurry containing about 5 weight percent alumina. Glacial acetic acid was added to this slurry to theextent of 6 weight percent based on alumina and the resulting slurry was dried for twenty-four hours inasteam oven (250" F.). The recovered dry gel was, 1000 grams of dry alumina was ground to a powder, treated with 85.2 grams of ammonium meta vanadate dissolved. in 1400 grams of hot water. The resulting paste was well mixed and dried in a steam oven. drying,;the po,wder was reimpregnated with another 85,2 grams ofammonium meta vanadate as above and again dried to give a final composition of 10% V205 on alumina. The catalyst was activated by heating at 850 F. overnight prior to use.

Similarly, catalysts can be prepared from alumina obtainedfrom other sources, such as by precipitation from aqueous solutions of alumina nitrate, chloride, etc., by the addition of ammonium hydroxide;

The impregnation of the hydrous gel.(see Example II) wascarried out in an analogous. manner except that the gel was, not dried prior to impregnation.

Example-I Thathighjsulfur removal by hydrogen transfer is apparently specific to the vanadia-alumina system and is not shown by vanadia supported on other carriers, oralumina alone, is demonstrated by the following data.

A mixture off'10' volume percent thiophene in methyl cycl heX-ane was. passed through a vaporizer and preheate" andthe vapors passed over the respective catalyst bed at a temperature of 800" F. and a pressure of 200 After analyzed for sulfur. The catalyst compositions in these ruiis were all prepared by impregnation of the hydrous ge s.

Wt. Percent Sulfur Percent Catalyst Sulfur Decrease Feed Product 10% V105 on A110; 4.9 1. 2 75 4. 2 3. 3 21 4.9 1.4 71 it 5'3 100% A110; 41 1 31 9 Example ll That the method of preparation of the catalyst is a very important factor in its activity as a hydrogen transfer desulfurizing catalyst is shown by the following data. The catalyst produced by the dry impregnation of the gel was considerably more active than that prepared by impregnation of the hydrous gel. The reaction conditions of Example I were employed.

Product Dist., Wt. Percent Percent Catalyst (10% V105 on Wt. Percent Sulfur Sulfur A1203) Reduction Gas Coke Oil Feed Prod.

Impregnated Dry Gel-.." 2. 7 1.0 96. 3 4. 2 0. 5 88 Impregnated Hydrous Gel 11.7 0.7 87. 6 4. 9 1.2 75

The following data show the superiority of the V205-A1203 catalyst over activated carbon, which is also a hydrogen transfer catalyst, and over a molybdena-alumina catalyst, which is a known efficient hydrogenationdehydrogenation catalyst. The feeds and the reaction conditions are the same as those previously employed. The vanadia-chromia and molybdena catalysts were prepared by impregnation of the dry gel.

Prod. Dist., Wt. percent Percent Wt. percent Sulfur Sulfur Catalyst Reduction Gas Coke Oil Feed Prod.

10% V205 on A1203 2 7 1. 96. 3 4. 2 0. 88 M00; 0n A1103" 19 0 2.0 79.0 4. 2 1. 2 71 10% C110; 0n AlzOa 7.4 1. 3 91. 3 4. 2 1.8 57 Activated Carbon 4. 2 1. 1 74 The superior results obtained not only in desulfurization, but in product yield and low coke and gas formation, by the vanadia catalyst as opposed to the results obtained with molybdena and chromia, coupled with the known dehydrogenation-hydrogenation properties of the latter, serve to point out that the reaction with V205 is not merely a catalytic dehydrogenation followed by hydrogenation, but an actual hydrogen transfer reaction.

Example IV T 0 determine the effectiveness of this method of desulfurizing upon refinery streams, a heavy naphtha containing 0.66 wt. percent thiophene sulfur and a naphthene 6 content of 40 vol. percent was passed over a catalyst consisting of 10% V205 on A1203 at 0.5 v./v./hr. under a pressure of 200 p. s. i. g. at 800 F. After caustic washing, the oil product had a sulfur content of 0.17, equivalent to a 74% reduction in sulfur.

Similarly, a kerosene cut containing 5.2% of thiophone type sulfur was treated as above, and an oil product containing 1.7% residual sulfur, equivalent to a 70% reduction, was obtained. Both examples were oncethrough operations and recycling would have substantially further decreased the sulfur content.

The process of the invention admits of many modifications obvious to those skilled in the art. Thus, the hydrogen donating naphthene may be present initially in the stream being treated. In these cases, it is not necessary to add extraneous naphthenes. Where there is only a relatively small amount of naphthenes present, it is desirable to add extraneous naphthenes, such as cyclohexane and cyclopentane, and their homologues and analogues.

What is claimed it:

1. A process for catalytic desulfurization of hydrocarbons containing ring sulfur which comprises reacting in the vapor phase, a gaseous mixture containing added naphthenes and hydrocarbons containing ring sulfur in the presence of a hydrogen transfer gel type catalyst consisting essentially of vanadium oxide supported on alumina, prepared by impregnating dry alumina gel with a water soluble vanadium compound followed by thermal conversion of said compound to vanadium oxide and thereafter activating the catalyst by heating at elevated temperatures, at temperatures of between about 750 to about 950 F.

2. A process for the catalytic removal of ring sulfur from sulfur-containing hydrocarbons which comprises vaporizing said hydrocarbons, forming a gaseous stream containing said vapors in the presence of a vaporized naphthenic hydrocarbon and in the substantial absence of added free hydrogen, passing said gaseous stream at a temperature of between 750 to about 950 F. in contact with a hydrodesulfurization catalyst prepared by impregnating dry alumina gel with a vanadium-containing compound followed by the thermal conversion of said vanadium compound to vanadium oxide and thereafter activating the catalyst by a heat treatment, transferring hydrogen from said naphthenic compound to said hydrocarbons containing ring sulfur by the catalytic action of said vanadium catalyst whereby said ring sulfur is removed from said hydrocarbons and said naphthenic hydrocarbon is converted at least partly to aromatic hydrocarbons.

3. The process of claim 2 wherein said catalyst contains about 10% V205.

4. The process of claim 2 wherein said sulfur removal is carried out at superatmospheric pressures.

5. The process of claim 2 wherein additional naphthenic compounds are extraneously added to said naphtha.

References Cited in the file of this patent UNITED STATES PATENTS 2,075,171 Buell et al Mar. 30, 1937 2,253,308 Rosen Aug. 19, 1941 2,324,066 Connolly July 13, 1943 2,324,067 Connolly July 13, 1943 2,372,084 Jones Mar. 20, 1945 2,498,559 Layng et a1 Feb. 21, 1950 2,500,146 Fleck et a1 Mar. 14, 1950 2,547,380 Fleck Apr. 3, 1951 2,573,726 Porter et al. Nov. 6, 1951 2,591,525 Engel Apr. 1, 1952 2,640,802 Porter et al June 2, 1953 

1. A PROCESS FOR CATALYTIC DESULFURIZATION OF HYDROCARBONS CONTAINING RING SULFUR WHICH COMPRISES REACTING IN THE VAPOR PHASE, A GASEOUS MIXTURE CONTAINING ADDED NAPHTHENES AND HYDROCARBONS CONTAINING RING SULFUR IN THE PRESENCE OF A HYDROGEN TRANSFER GEL TYPE CATALYST CONSISTING ESSENTIALLY OF VANADIUM OXIDE SUPPORTED ON ALUMINA, PREPARED BY IMPREGNATING DRY ALUMINA GEL WITH A WATER SOLUBLE VANADIUM COMPOUND FOLLOWED BY THERMAL CONVERSION OF SAID COMPOUND TO VANADIUM OXIDE AND THEREAFTER ACTIVATING THE CATALYST BY HEATING AT ELEVATED TEMPERATURES, AT TEMPERATURES OF BETWEEN ABOUT 750* TO ABOUT 950* F. 